Separators currently used in lead acid (or storage) batteries are microporous films of sheet material that prevent shorting between neighbouring electrode plates of opposite polarities and plate material from falling out, but on account of their porous structure permit ionic current flow in the electrolyte. Separators of this kind are known from, for example, U.S. Pat. Nos. 3,351,495, 4,927,722, and 5,776,630 and from, for example, WO publication WO 2001/013,442, each hereby incorporated herein by reference. Typical polymers these separators are made from include polyolefins such as high molecular weight polyethylene (e.g., ultra high molecular weight polyethylene, UHMWPE). Such separators may include a filler and are normally provided on at least one side with longitudinal ribs that are intended to prevent direct contact of the flat sheet material with the positive electrode plate and maintain the spacing between the opposing electrodes. These ribs also lend the separator a certain rigidity in the longitudinal direction. Longitudinal ribs of this kind are typically formed by feeding the precursor between a grooved calender roll and a smooth surface calender roll.
Separators are usually manufactured by slot die extrusion of a thermoplastic into a film (or precursor) that is then calender rolled into a sheet material with the prescribed ribs, after which the pore former, such as mineral oil, is extracted and the porous sheet material or web is wound into rolls. This porous sheet material is later drawn off the roll and cut into strips of the desired width. These strips are cut to the desired length to form separator pieces (or leaves) or to form lengths that are then folded over either a positive or a negative electrode plate to form an envelope, the two peripheral regions of which can be joined by, for example, heat sealing, pressure welding or other processes that are known to form a pocket or envelope. Electrode plates are then assembled into groups for a storage battery, plates in separator envelopes alternating with plates of opposite polarity without envelopes. In general, only electrode plates of a single polarity are placed in envelope separators; in special cases, however, electrode plates of both polarities can be placed in envelope separators. The electrode plates within a group are aligned and then joined together.
The alignment of the electrode plates may result in individual electrode plates being pushed to a greater or lesser extent into one or the other peripheral region of an envelope separator. Because the electrode plates frequently acquire pointed tips or sharp edges depending on the manufacturing process, this displacement can cause a point or edge of an electrode plate to puncture the separator material, which in turn can result in shorting with the neighbouring electrode. This is especially the case when the electrode plates used consist of a grid of, for example, expanded or stamped metal into which the actual active material is incorporated, as described for example in EP published application EP-A-0 994 518. In such cases it may occur that the expanded material is not cut precisely at the nodes, so that individual grid wires project from the electrode plates, bend slightly on alignment of the electrode plates and puncture the thin sheet material of the separator.
As such, there exists a need for improved, new, modified, or more robust separators and/or envelopes, improved, new, or modified separator and/or envelope manufacturing processes, improved, new, modified, or more robust batteries including such separators, envelopes, and/or the like for at least certain applications, uses, efficiencies, and/or the like.